Radio communication between a transmitter and a receiver, one of which is mobile, is made difficult by the fact that radio waves going from the transmitter to the receiver travel simultaneously along a multitude of paths of different lengths, and are subject to numerous reflections, and by the fact that these various paths themselves vary over time as a function of movements of the mobile or as a function of changes to the immediate environment of the mobile (in particular: vehicles travelling close to the mobile).
As a result, the signal picked up on arrival is constituted by the superposition of a multitude of signals that are phase-shifted relative to one another and that correspond respectively to the different paths along which the radio wave has travelled between the transmitter and the receiver, such that: firstly the signal as picked up is difficult to decode; and secondly interference phenomena occur which, in certain particular positions of the receiver antenna, can cause the signal as picked up to cancel out completely.
In an attempt to remedy those drawbacks, several palliatives are known:
transmitter power can be increased at the mobile and at the base, however, that disposition is not very effective since it also increases the level of noise due to the multiple reflections of the radio signal, and in addition it is difficult to apply at the mobile end where any increase in transmitter power gives rise to an increase in weight and bulk and to a decrease in battery life; PA1 it is also possible to multiply the number of bases so that radio communication is always taking place over a short distance between each mobile and one of the bases, however that solution is expensive; and PA1 it is also known to make use at the base of a multitude of synchronized antennas organized in an array, thereby making it possible to reduce problems due to destructive interference, but that does not improve the signal-to-noise ratio of the signal as picked up and it does not take account of variations in the electro-magnetic environment. PA1 .times. designates the convolution product; PA1 t designates time; and PA1 h'.sub.i (-t) is an approximation to the time reversal of the impulse response h.sub.i (t) between the antenna i and the mobile, said impulse response being such that when a radio signal E(t) is transmitted by one of the antenna and the mobile, the other of said two elements receives a signal R(t) =h.sub.i (t).times.E(t); PA1 the corrected signal S'.sub.i (t) then being either transmitted to the mobile by the antenna in question if the signal S.sub.i (t) is a transmit signal, or else being combined with the other signals as received by the other antennas of the base, if the signal S.sub.i (t) is a receive signal. PA1 the method includes the following steps: PA1 during step a), the approximation h'.sub.i (t) of the impulse response specific to each antenna is determined on the basis of a predetermined radio signal transmitted by the mobile, said step a) being performed at regular time intervals for each mobile; PA1 steps a) and b) are performed once and for all, for a given geographical area, step a) consisting in transmitting at least one predetermined radio signal successively from a plurality of points k in the area under consideration, thereby determining a series of approximations h'.sub.ik (t) of the impulse response h.sub.ik (t) between each point k and each antenna i of the base, and then in computing the approximation h'.sub.i (t) using the formula h'.sub.i (t)=.SIGMA..sub.k a.sub.k h'.sub.ik (t), where the terms a.sub.k designate weighting coefficients, said approximation h'.sub.i (t) subsequently being used in step c) for processing the signals transmitted to or received from any mobile located in the above-mentioned given area; PA1 the base covers a plurality of above-mentioned areas, a series of approximations h'.sub.i (t) to the impulse response being determined once and for all in steps a) and b) for each of the above-mentioned areas, and step c) is implemented successively at least at the beginning of each call between a base and each mobile, respectively with each of the series of approximations h'.sub.i (t) corresponding respectively to the various areas, determining on each occasion a corrected signal S'.sub.i (t) from a signal S.sub.i (t) received from the mobile under consideration, and then determining which series of approximations h'.sub.i (t) corresponding to a given area optimizes the combination of corrected signals S'.sub.i (t), said series of approximations h'.sub.i (t) subsequently being used to correct the signals transmitted to or received from the mobile under consideration; PA1 the radio signals normally transmitted by the base are modulated signals having a carrier frequency f0, the signals normally transmitted by the mobile are modulated signals having a carrier frequency f1 that is different from f0, and the steps a) and b) are performed as follows: PA1 the radio signals normally transmitted by the base (1) are modulated signals at a carrier frequency f0, the method including the following additional steps: PA1 the signal to be corrected S.sub.i (t) is a modulated signal having a determined carrier frequency f, said signal being modulated over a range of frequencies of width that is less than 1% of the carrier frequency f, the method including the following steps: PA1 the signal to be corrected S.sub.i (t) is a modulated signal having a determined carrier frequency f, said signal being modulated over a range of frequencies of width that is less than 1% of the carrier frequency f, the method including the following steps: PA1 the base covers a plurality of the above-mentioned areas, a series of values H.sub.i (f) for the transfer function being determined in step d) for each of the above-mentioned areas, and in which step e) is implemented at least at the beginning of each call between the base and each mobile, with each series of approximations H.sub.i (f) corresponding to respective different areas, by determining on each occasion a corrected signal S'.sub.i (t) from a signal S.sub.i (t) received from the mobile under consideration, and then determining which series of values H.sub.i (f) corresponding to a given area optimizes the combination of corrected signals S'.sub.i (t), said series of values H.sub.i (f) subsequently being used in step e) to correct the signals transmitted to or the signals received from the mobile under consideration; and PA1 the radio signals normally transmitted by the base are modulated signals having a carrier frequency f0, the signals normally transmitted by a mobile being modulated signals having a carrier frequency f1 different from f0, and step d) is performed as follows: